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| United States Patent |
5,280,072
|
|
Wamprecht
, et al.
|
January 18, 1994
|
Epoxide and anhydride groups-containing copolymer with polyol
Abstract
The present invention relates to coating compositions in pulverulent form
which are solid below 30.degree. C. and liquid above 150.degree. C. and
contain
A) 10 to 99 parts by weight of a copolymer component containing at least
one copolymer which is prepared from olefinically unsaturated compounds,
has a weight average molecular weight of 1500 to 75,000 and contains in
chemically bound form
(i) 1 to 30% by weight of cyclic carboxylic acid anhydride groups
(calculated as C.sub.4 H.sub.2 O.sub.3) and
(ii) 0.3 to 10% by weight of epoxide groups (calculated as C.sub.2 H.sub.3
O), and
B) 1 to 90 parts by weight of a polyol component containing at least one
organic polyol having at least two hydroxyl groups per molecule,
provided that for every anhydride group of component A) there are 0.1 to 10
hydroxyl groups of component B).
| Inventors:
|
Wamprecht; Christian (Neuss, DE);
Kreuder; Hans-Joachim (Toenisvorst, DE);
Pedain; Josef (Cologne, DE)
|
| Assignee:
|
Bayer Aktiengesellschaft (Leverkusen, DE)
|
| Appl. No.:
|
879251 |
| Filed:
|
May 5, 1992 |
Foreign Application Priority Data
| Current U.S. Class: |
525/207; 525/128; 525/131; 525/148; 525/176; 525/187; 525/934 |
| Intern'l Class: |
C08L 033/14; C08L 075/02; C08L 075/04; C08L 067/02 |
| Field of Search: |
525/207,128,131,148,176,87,934
|
References Cited
U.S. Patent Documents
| 3784396 | Jan., 1974 | Fourment et al. | 117/21.
|
| 3914333 | Oct., 1975 | Labana et al. | 525/207.
|
| 3991132 | Nov., 1976 | Siwiec et al. | 260/836.
|
| 3991133 | Nov., 1976 | Siwiec et al. | 260/836.
|
| 4069275 | Jan., 1978 | Labana et al. | 260/836.
|
| 4101606 | Jul., 1978 | Cenci et al. | 260/857.
|
| 4442145 | Apr., 1984 | Probst et al. | 427/385.
|
| 4861841 | Aug., 1989 | Marrion | 525/327.
|
| Foreign Patent Documents |
| 73022 | Mar., 1983 | EP.
| |
| 473999 | Mar., 1992 | EP.
| |
| 52-069936 | Jun., 1977 | JP.
| |
Other References
Chem Abstract 88(12):75374a.
Detroit Society for Paint Technology, "Ponder Coating: Why-How-When,"
Journal of Paint Technology, vol. 44, No. 565, Feb. 1972, pp. 30-37.
|
Primary Examiner: Sellers; Robert E.
Attorney, Agent or Firm: Gil; Joseph C., Roy; Thomas W.
Claims
What is claimed is:
1. A coating composition in pulverulent form which is solid below
30.degree. C. and liquid above 50.degree. C. and comprises
A) 10 to 99 parts by weight of copolymer component containing at least one
copolymer which is prepared from olefinically unsaturated compounds, has a
weight average molecular weight of 1500 to 75,000 and contains in
chemically bound form
(i) 1 to 30% by weight of cyclic carboxylic acid anhydride groups
(calculated as C.sub.4 H.sub.2 O.sub.3) and
(ii) 0.3 to 10% by weight of epoxide groups (calculated as C.sub.2 H.sub.3
O), and
B) 1 to 90 parts by weight a polyol component containing at least one
organic polyol having at least two hydroxyl groups per molecule, provided
that if said polyol component contains a acrylic copolymer, said acrylic
copolymer is prepared from olefinically unsaturated monomers consisting
essentially of the reaction product of hydroxyl group-containing monomers
with comonomers which are free from functional groups, and
provided that for every anhydride group of component A) there are 0.1 to 10
hydroxyl group of component B).
2. The coating composition of claim 1 wherein component A) comprises the
reaction product of
a) 1 to 30 parts by weight of copolymerized monomers containing anhydride
groups,
b) 1 to 66 parts by weight of copolymerized monomers containing epoxide
groups and
c) 4 to 98 parts by weight of copolymerized non-functional monomers which
are free from anhydride groups and epoxide groups.
3. The coating composition of claim 2 wherein monomer a) comprises maleic
anhydride and/or itaconic anhydride.
4. The coating composition of claim 2 wherein monomer b) comprises glycidyl
acrylate, glycidyl methacrylate and/or allyl glycidyl ether.
5. The coating composition of claim 3 wherein monomer b) comprises glycidyl
acrylate, glycidyl methacrylate and/or allyl glycidyl ether.
6. The coating composition claim 1 wherein said organic polyol of component
B) has a number average molecular weight of greater than 261 and comprises
a member selected from the group consisting of acrylic copolymers,
polyethers, polyesters, urea-modified polyurethanes, polyurethanes,
polyureas and polycarbonates.
7. The coating composition of claim 2 wherein said organic polyol of
component B) has a number average molecular weight of greater than 261 and
comprises a member selected from the group consisting of acrylic
copolymers, polyethers, polyesters, urea-modified polyurethanes,
polyurethanes, polyureas and polycarbonates.
8. The coating composition of claim 5 wherein said organic polyol of
component B) has a number average molecular weigh of greater than 261 and
comprises a member selected from eh group consisting of acrylic
copolymers, polyethers, polyesters, urea-modified polyurethanes,
polyurethanes, polyureas and polycarbonates.
9. The coating composition of claim 1 wherein component B) comprises an
organic polyol having a molecular weight of 104 to 261 and containing 2 to
6 hydroxyl groups per molecule.
10. The coating composition of claim 2 herein component B) comprises an
organic polyol having a molecular weight of 104 to 261 and containing 2 to
6 hydroxyl groups per molecule.
11. The coating composition of claim 5 wherein component B) comprises an
organic polyol having a molecular weight of 104 to 261 and containing 2 to
6 hydroxyl group per molecule.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to powder coating compositions which are solid at
temperatures below 30.degree. C. and liquid above 150.degree. C. and which
are based on A) copolymers containing carboxylic acid anhydride groups and
epoxide groups and B) polyhydroxyl compounds.
2. Description of the Prior Art
It is known to use compositions containing polyacrylates having at least
two carboxyl groups per molecule and polyepoxide compounds, optionally
based on acrylates, as powder lacquers. Japanese Patent Application
73-9,319 (Publication number: 49-116,134; Chem. Abs. 82(24):157882e)
describes heat curable powder coating compositions containing A) a solid
acrylate resin prepared by the reaction of a hydroxyl group-containing
copolymer with a polycarboxylic acid or its anhydride and B) an epoxide
group-containing copolymer. The two polymers are mixed together as melts
at temperatures of about 100.degree. C. and the mixtures are ground up
after cooling. The coatings may be applied to metal surfaces and hardened
at temperatures of about 200.degree. C.
DE-OS 23 47 680 describes heat curable powder lacquers containing A) 50 to
97% of an epoxide group-containing copolymer having a molecular weight of
3,000 to 15,000 and a softening point of 80.degree. to 150.degree. C. and
B) 3 to 50% of a carboxyl group-containing hardener having a softening
point of at least 50.degree. C., wherein the hardener may be a copolymer
containing carboxyl groups.
Japanese Patent Application 75-146,705 (Publication Number: 52-069,936;
Chem. Abs. 88(12):73374a) describes heat curable powder lacquers based on
glycidyl (meth)acrylate copolymers containing A) 100 parts of a copolymer
(T 30.degree. to 100.degree. C., molecular weight 3,000 to 70,000)
containing 10 to 50% by weight of glycidyl(meth)acrylate, 30 to 85% by
weight of acrylic acid C.sub.1 -C.sub.12 -alkyl esters and 0 to 60% by
weight of another comonomer, B) 0.1 to 30 parts of a copolymer which
regulates flow properties (T.sub.g >50.degree. C., molecular weight
>1000), containing 30 to 85% by weight of (meth)acrylic acid alkyl esters,
1 to 50% by weight of a monomer having a glycidyl, carboxyl, hydroxyl or
amide group and 0 to 69% by weight of another monomer and C) 3 to 55 parts
of an aliphatic dicarboxylic acid having 4 to 20 carbon atoms. The
lacquers adhere firmly to metals without previous surface treatment.
U.S. patent Ser. No. 3,991,132 and U.S. patent Ser. No. 3,991,133 describe
heat curable powder lacquers obtained from A) an epoxide-containing
copolymer containing 5 to 20% of glycidyl methacrylate and 80 to 95% of
other comonomers (T.sub.g 40.degree. to 90.degree. C., molecular weight
1500 to 15,000) and B) an anhydride cross-linking agent, either a
dicarboxylic acid anhydride or a dicarboxylic acid anhydride homopolymer,
provided that the copolymer is difunctional. In U.S. patent Ser. No.
3,991,132 the copolymer is synthesized from at least 2 to 10% of an
unsaturated acid amide and in U.S. patent Ser. No. 3,991,133 the copolymer
is synthesized from at least 2 to 10% of a C.sub.5 -C.sub.7 -
hydroxyalkyl(meth)acrylate in addition to 70 to 93% of other comonomers
such as methyl or butyl methacrylate, styrene or vinyl toluene. Further, a
quantity of the anhydride hardeners is replaced by a hydroxycarboxylic
acid so that 0.1 to 0.4 carboxyl groups of the hydroxycarboxylic acid are
present for every functional group of the copolymer.
It is also known to use components containing anhydride groups with
components containing hydroxyl groups as powder lacquers. Lacquer systems
of this type are described in U.S. Pat. Nos. 4,069,275 and 4,101,606,
British Patents Nos. 1 366 081 and 1 561 828 and European Patent
Applications Nos. 73 022 and 209 377. Such powder lacquers are normally
hardened at temperatures of 130.degree. to 200.degree. C., but it has been
found that the cross-linking reactions do not proceed to completion at
relatively low temperatures, e.g., 130.degree. to 160.degree. C., so that
the solvent resistance of the lacquer films obtained is not sufficient. it
is only at hardening temperatures of 170.degree. to 200.degree. C. that
lacquer films with acceptable solvent resistance are obtained.
In none of the previously described publications are copolymers containing
both cyclic carboxylic acid anhydride groups and epoxide groups described
as binders or powder lacquers.
It has now surprisingly been found that copolymers of olefinically
unsaturated compounds containing both cyclic carboxylic acid anhydride
groups and epoxide groups in the same macromolecule are excellent binders
for powder lacquers when used in combination with polyels if they have the
required softening point or range. The special advantage of such binder
compositions is that they enable solvent-resistant lacquer films to be
obtained at low stoving temperatures, e.g., at 130.degree. to 150.degree.
C.
Another advantage lies in the fact that initially component A) does not
contain free carboxyl groups which are required for cross-linking with the
epoxide groups of component A). The required carboxyl groups are
subsequently formed by the reaction of the carboxylic acid anhydride
groups of component A) with the hydroxyl groups of component B). These new
binder compositions therefore have considerably better storage stability
at room temperature than comparable state of the art systems containing
carboxyl groups.
Due to the high cross-linking densities which may be obtained, powder
coatings having a very high level of chemical and solvent resistance can
be obtained from the binder compositions according to the invention.
The binder compositions according to the invention therefore on the one
hand have excellent storage stability at room temperature or at moderately
elevated temperatures below their softening range and on the other hand
result in coatings having excellent properties.
SUMMARY OF THE INVENTION
The present invention relates to coating compositions in pulverulent form
which are solid below 30.degree. C. and liquid above 150.degree. C. and
contain
A) 10 to 99 parts by weight of a copolymer component containing at least
one copolymer which is prepared from olefinically unsaturated compounds,
has a weight average molecular weight of 1500 to 75,000 and contains in
chemically bound form
(i) 1 to 30% by weight of cyclic carboxylic acid anhydride groups
(calculated as C.sub.4 H.sub.2 O.sub.3) and
(ii) 0.3 to 10% by weight of epoxide groups (calculated as C.sub.2 H.sub.3
O), and
B) 1 to 90 parts by weight of a polyol component containing at least one
organic polyol having at least two hydroxyl groups per molecule,
provided that for every anhydride group of component A) there are 0.1 to 10
hydroxyl groups of component B).
DETAILED DESCRIPTION OF THE INVENTION
German Patent Application P 4 027 609.0 (which corresponds to copending
application U.S. Ser. No. 07/748,297, filed Aug. 21, 1991) is directed to
compositions containing A) copolymers having both cyclic carboxylic acid
anhydride groups and epoxide groups and B) polyols, but these binder
compositions are used exclusively as binders for liquid, in particular
solvent-containing lacquers. The copending application does not disclose
the possibility of using such or similar compositions as binders for
powder coating compositions.
In the context of the present invention "pulverulent compositions" means
both mixtures of pulverulent copolymers A) with pulverulent polyhydroxyl
compounds B) and "mixed powders" in which the individual powder particles
already contain the individual components A) and B). The auxiliary agents
and additives C) optionally used may be present as separate component in
the mixture or they may have been incorporated in the pulverulent binder
compositions AB or the pulverulent binder components A) and/or B) during
preparation of the binder compositions or components.
The compositions to be used according to the invention are solid below
30.degree. C., preferably below 35.degree. C., and liquid above
150.degree. C., preferably above 120.degree. C.
Copolymer component A) contains at least one copolymer containing both
cyclic carboxylic acid anhydride groups (calculated as C.sub.4 H.sub.2
O.sub.3) in a quantity of I to 30% by weight, preferably 5 to 25% by
weight, and chemically incorporated epoxide groups (calculated as C.sub.2
H.sub.3 O) in a quantity of 0.3 to 20% by weight, preferably 1 to 15% by
weight. The copolymers have a weight average molecular weight (M.sub.w, as
determined by gel permeation chromatography using polystyrene as standard)
of 1,500 to 75,000, preferably 2,000 to 60,000 and more preferably 3,000
to 40,000.
The copolymers are based on monomers which are preferably monoolefinically
unsaturated. Three groups of olefinically unsaturated monomers may be used
for the preparation of the copolymers, i.e.:
a) olefinically unsaturated monomers containing anhydride groups,
b) olefinically unsaturated monomers containing epoxide groups and
c) non-functional olefinically unsaturated monomers which are free from
anhydride groups and epoxide groups.
Monomers a) are generally used in a quantity of 1 to 30 parts by weight,
preferably from 5 to 25 parts by weight; monomers b) in a quantity of 1 to
66 parts by weight, preferably 3 to 50 parts by weight; and monomers c) in
a quantity of 4 to 98 parts by weight, preferably 25 to 92 parts by
weight, wherein the sum of the parts by weight of a) to c) add up to 100.
In the context of the present disclosure, the proportions of the individual
monomers in the mixture to be copolymerized are calculated so that the
copolymers contain the above mentioned quantities of chemically
incorporated anhydride groups and epoxide groups. The quantity of these
groups present in the copolymers corresponds to the quantity of the same
groups present in the monomer mixture since it is assumed that the
copolymers correspond in their chemical composition to the chemical
composition of the monomer mixture.
Monomers a) are mono-olefinically unsaturated carboxylic acid anhydrides
such as maleic acid anhydride or itaconic acid anhydride. Maleic acid
anhydride is preferred.
Monomers b) are mono-olefinically unsaturated epoxides such as glycidyl
acrylate, glycidyl methacrylate and allyl glycidyl ether. The former two
are preferred.
Monomers c) preferably have a molecular weight of 86 to 400. They are
non-functional, preferably mono-olefinically unsaturated monomers which
are free from anhydride groups and epoxide groups and include the monomers
disclosed in the previously mentioned references. Examples include esters
of acrylic and methacrylic acid such as methyl acrylate, ethyl acrylate,
n-butyl acrylate, isobutyl acrylate, tert.-butyl acrylate, 2-ethylhexyl
acrylate, cyclohexyl methacrylate, methyl methacrylate, n-butyl
methacrylate, isobutyl methacrylate and 2-ethyl hexyl methacrylate;
aromatic vinyl compounds such as styrene, vinyl toluene,
.alpha.-methylstyrene, .alpha.-ethylstyrene and diethylstyrenes,
isopropylstyrenes, butylstyrenes and methoxystyrenes which are substituted
in the nucleus and may optionally be in the form of isomeric mixtures;
vinyl ethers such as ethyl vinyl ether , n-propyl vinyl ether, isopropyl
vinyl ether , n-butyl vinyl ether and isobutyl vinyl ether ; and vinyl
ester such as vinyl acetate, vinyl propionate and vinyl butyrate.
Mixtures of monomers a) to c) may also be used for the copolymerization,
provided that the monomers used for the preparation of the copolymers are
chosen so that the resulting copolymers are solid at temperatures below
30.degree. C. al,. at temperatures above 150.degree. C. This means that
the copolymers have a glass transition temperature, T. of 30.degree. to
100.degree. C., preferably 35.degree. to 80.degree. C., as determined by
differential thermoanalysis (DTA). This requirement for the glass
transition temperature is fulfilled if a suitable ratio of "plasticizing"
monomers (which lower the glass transition temperature of the copolymers)
to "hardening" monomers (which raise the glass transition temperature) are
used in the preparation of the copolymers.
Examples of "plasticizing" monomers include alkyl esters of acrylic acid
such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl
acrylate, 2-ethylhexyl acrylate, lauryl acrylate and ethyl diglycol
acrylate; vinyl esters such as vinyl propionate; and vinyl ethers such as
vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, vinyl isobutyl
ether, vinyl octadecyl ether and vinyl cyclohexyl ether.
Examples of "hardening" monomers include alkyl esters of methacrylic acid
such as methyl methacrylate, ethyl methacrylate, isobutyl methacrylate,
cyclohexyl methacrylate, 2-phenyl ethyl methacrylate, tetrahydrofurfuryl
methacrylate, isopropyl methacrylate, tert.-butyl methacrylate, neopentyl
methacrylate, isobornyl methacrylate and benzyl methacrylate; aromatic
vinyl compounds such as styrene, vinyl toluene and .alpha.-ethyl styrene;
and heterocyclic vinyl compounds such as vinyl pyrrolidone, vinyl
caprolactam and vinyl carbazole.
The copolymers may be prepared by copolymerization of the above exemplified
monomers a) to c) by conventional radical polymerization processes such as
solvent-free or solution polymerization. In these processes, the monomers
are copolymerized in the presence of radical formers and optionally
molecular weight regulators at temperatures of 60.degree. to 160.degree.
C., preferably 80.degree. to 150.degree. C.
The copolymers are preferably prepared in inert solvents. Suitable solvents
include aromatic compounds such as benzene, toluene and xylene; esters
such as ethyl acetate, butyl acetate, hexyl acetate, heptyl acetate,
methyl glycol acetate, ethyl glycol acetate and methoxy propyl acetate;
ethers such as tetrahydrofuran, dioxane and diethylene glycol
dimethylether; and ketones such as acetone, methyl ethyl ketone, methyl
isobutyl ketone, methyl-n-amyl ketone and methyl isoamyl ketone. Mixtures
of these solvents may also be used.
Preparation of the copolymers may be carried out continuously or
discontinuously. The monomer mixture and the initiator are generally
introduced continuously at a uniform rate into a polymerization reactor
and the corresponding quantity of polymer is removed continuously at the
same time. Copolymers which are substantially chemically uniform may
advantageously be produced by this method. Copolymers of this type may
also be prepared by introducing the reaction mixture at a constant rate
into a stirred vessel without removal of the polymer. Alternatively, part
of the monomers may be introduced into the reaction vessel, for example in
solvents of the type mentioned above, and the remaining monomers and
auxiliary agents may then be added separately or together at the reaction
temperature.
The polymerization is generally carried out at atmospheric pressure, but
pressures of up to 25 bar may be employed. The initiators are used in
quantities of 0.05 to 15% by weight, based on the total quantity of
monomers.
The initiators include known radical intiators, e.g., aliphatic azo
compounds such as azodiisobutyric acid nitrile,
azo-bis-2-methylvaleronitrile, 1,1'-azo-bis-l-cyclohexane nitrile and
2,2'-azo-bis-isobutyric acid alkyl esters; symmetrical diacyl peroxides
such as acetyl, propionyl and butyryl peroxide, benzoyl peroxides
substituted with bromine, nitro, methyl or methoxy groups, and lauryl
peroxides; symmetrical peroxydicarbonates such as diethyl, diisopropyl,
dicyclohexyl and dibenzoyl peroxydicarbonate;
tert.-butyl-peroxy-2-ethylhexanoate; tert.-butyl perbenzoate;
hydroperoxides such as tert.-butyl hydroperoxide and cumene hydroperoxide;
dialkyl peroxides such as dicumyl peroxide; tert.-butyl cumyl peroxide and
di-tert.-butyl peroxide.
Conventional regulators may be used in the process of preparation to
regulate the molecular weight of the copolymers. Tert.-dodecylmercaptan,
n-dodecylmercaptan and diisopropyl xanthogen disulphide are examples of
such regulators. The regulators may be added in quantities of 0.1 to 10%
by weight, based on the total quantity of monomers.
The solutions of copolymers obtained from copolymerization may be
transferred without further working up to the evaporation or
degasification process in which the solvent is removed, for example in an
evaporation extruder
t 120.degree. to 160.degree. C. under a vacuum of 100 to 300 mbar; the
copolymers to be used according to the invention are obtained.
Component B) consists of at least one organic compound having at least two
hydroxyl groups per molecule and a glass transition temperature, T.sub.g,
or a melting point within the range of 0.degree. to 150.degree. C.,
preferably 30.degree. to 150.degree. C. and more preferably 35.degree. to
120.degree. C. Preferred compounds used as component B) include those
which have (on statistical average) from 2 to 50, preferably 2 to 10 and
more preferably 2 to 6 hydroxyl groups per molecule.
Compounds having a glass transition temperature below 30.degree. C. or a
melting point below 30.degree. C. as well as compounds which are liquid at
room temperature may be used when combined with high melting copolymers A)
to form compositions AB which are solid at temperatures above 30.degree.
C. These compositions are preferably prepared using extruders or kneaders
and can be converted into powders even when liquid components B) are used.
The compounds used as component B) include compounds having a number
average molecular weight (M.sub.n) above 261, preferably 262 to 15,000 and
more preferably 262 to 1000, and which conform to the above-mentioned
conditions concerning the melting points and hydroxyl group content.
Examples include hydroxy functional acrylic copolymers, hydroxy functional
polyethers, hydroxy functional polyesters, optionally urea-modified
hydroxy functional polyurethanes, hydroxy functional polyureas, hydroxy
functional polycarbonates and mixtures of such hydroxy functional
compounds.
Suitable compounds include hydroxyl group-containing polyureas obtained by
reacting diisocyanates such as
1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl cyclohexane (IPDI) with
amino alcohols such as 2-amino-ethanol or 1-amino-2-propanol in a molar
ratio of 1:2; polyether polyols such as the reaction product of 1 mole of
bisphenol A and 2 moles of propylene oxide; urea group-containing
polyurethanes such as the reaction product of 2 moles of IPDI with 1 mole
of a diol such as hexane-1,6-diol and 2 moles of an amino alcohol such as
1-amino-2-propanol; hydroxyl group-containing polyurethanes such as the
reaction product of 1 mole of
1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (IPDA) with 2 moles of
propylene carbonate or 2 moles of ethylene carbonate; copolymers of
olefinically unsaturated compounds prepared by the reaction of hydroxyl
group-containing monomers such as 2-hydroxyethyl-, 2-hydroxypropyl- or
2-hydroxybutyl(meth)-acrylate with comonomers which are free from
functional groups, such as those previously set forth, using a method of
preparation substantially analogous to that described above for the
preparation of component A).
Additional preferred polyol components B) are low molecular weight
polyhydroxyl compounds having a molecular weight of 104 to 261 containing
from 2 to 6 hydroxyl groups per molecule. Examples include
1,6-hexanediol,1,7-heptanediol1,2- and 1,8-octanediol-diol, 1,2- and
1,10-decanediol,2,2-bis-(4-hydroxycyclohexyl)propane,
1,1,1-tris-(hydroxymethyl)-propane,
N,N',N"-tris-(2-hydroxyethyl)-isocyanurate (THEIC),
2,2-bis-(hydroxy-methyl) -1,3-propanediol,
cis-1,2-bis-(hydroxymethyl)-cyclohexane,
4,4-bis-(hydroxymethyl)-cyclohexane, 2,5-bis-(hydroxy-methyl)-furan,
2,2'-bis-(hydroxymethyl)-biphenyl, bis-(hydroxy-ethyl)-malonic acid
diethylester, 2,2-bis-(hydroxymethyl)-5norbornene,
2-methyl-2-propyl-1,3-propanediol, 1,4-cyclohexanediol and
2,2-dimethyl-1,3-propanediol.
Components C) which may optionally be present in the powder coating
compositions according to the invention include the known auxiliary agents
and additives used in powder lacquer technology, e.g., pigments such as
titanium dioxide; levelling agents such as silicone compounds; and
catalysts.
Although the powder lacquers may be stoved without accelerating agents,
catalysts which catalyze the reaction between hydroxyl groups and
carboxylic acid anhydride groups and//or epoxide groups and carboxylic
acid groups may be used to reduce the stoving time and/or stoving
temperature. Examples of suitable catalysts include compounds containing
tertiary amino groups, such as 1,4-diaza-bicyclo-(2.2.2)-octane,
1,8-diazabicyclo-(5.4.0)-undec-7-ene, 1,5-diazabicyclo-(4.3.0)-non-5-ene,
1,2-dimorpholino-ethane and 1,3,5-tricyclohexyl hexahydro-1,3,5-triazine;
salts based on compounds containing tertiary amino groups and quaternary
ammonium groups such as (2-hydroxyethyl)-trimethylammonium chloride,
triethylamine hydrochloride, tetrabutylammonium chloride,
tetraethylammonium bromide, tetrahexylammonium chloride and
tetramethylammonium chloride; organic tin compounds such as tin dioctoate,
dibutyl tin laurate, dibutyl tin diacetate and dibutyl tin dichloride; and
phosphorus compounds such as triphenyl phosphine.
The pulverulent coating compositions may be prepared by various methods.
For example, the individual components A), B) and optionally C) may simply
be mixed together as powders. It is preferable, however, to homogenize the
solvent-free copolymers A), the solvent-free polyhydroxyl compounds B) and
the optionally used additives C) in the molten state in extruders or
kneaders at temperatures preferably from 100 to 120.degree. C. The
solidified product is ground and sieved to remove particles larger than
the desired particle size, for example, particles above 0.1 mm. No
significant reaction takes place at this time between the individual
components when this method is employed for preparing the powder coating
compositions. It is also possible in principle to prepare "mixed powders"
AB from components A) and B) by the above mentioned method and then to add
the optional auxiliary agents and additives in a further mixing process.
The nature and quantitative ratios of components A) and B) are preferably
chosen to provide 0.2 to 4, preferably 0.5 to 2 hydroxyl groups from
component B) and 0.1 to 8, preferably 0.2 to 4 and more preferably 0.4 to
1.5 epoxide groups from component A) for each acid anhydride group of
component A).
The pulverulent coating compositions may be applied to heat resistant
substrates by conventional powder application processes, e.g.,
electrostatic powder spraying or whirl sintering. The coatings may be
cured by heating to temperatures of 120.degree. to 220.degree. C.,
preferably 130.degree. to 200.degree. C. Hard, glossy, solvent-resistant
coatings having excellent corrosion protective properties and good color
stability in the presence of heat are obtained. According to the invention
the coating compositions may be used to coat any heat resistant substrates
such as glass, plastics and metals.
The parts and percentages given in the following examples are parts by
weight and percentages by weight unless otherwise indicated.
I General method of preparation for copolymers A.sub.1 to A.sub.4
containing carboxylic acid anhydride and epoxide groups and copolymers
B.sub.1 and B.sub.2 containing hydroxyl groups.
Part I was introduced into a 25-liter pressurized steel reactor equipped
with stirrer and cooling and heating devices and the contents were heated
to the reaction temperature. Part II (added over a total period of 3
hours) and Part III (added over a total period of 3.5 hours) were then
added in parallel. Stirring was continued for one hour at the given
temperature.
The polymer solutions obtained were completely freed from solvent in a
commercially available evaporation extruder at a temperature of about
150.degree. C., a dwell time of about 2 minutes and a vacuum of about 260
mbar and then cooled and granulated.
The reaction temperatures and the compositions of Parts I to III are set
forth in Table I together with the properties of the copolymers obtained.
The corresponding data for the hydroxyl group-containing copolymers
B.sub.1 and B.sub.2 are set forth in Table II.
TABLE I
______________________________________
Copolymers containing anhydride and
epoxide groups (quantities in g)
Copolymers A.sub.1 A.sub.2 A.sub.3
A.sub.4
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Part I
Toluene 9000 9000 9000 9000
Part II
Methyl methacrylate
3915 3915 3915 3915
n-butyl methacrylate
1470 1715
n-butyl acrylate 2445 2200
Styrene 1955 1955 1470 1715
Glycidyl methacrylate
980 735 735 735
Maleic acid anhydride
1470 1470 1225 1225
Part III
tert.-butylperoxy-2-
580 580 580 580
ethyl hexanoate (70%
in isododecane)
Toluene 630 630 630 630
Polymerization temper-
110 110 110 130
ature (.degree.C.)
Solids content (%)
50.4 50.6 50.4 49.9
Viscosity at 23.degree. C.
13260 14960 1090 550
(mPa.s)
Glass transition
83.4 84.1 61.8 58.9
temperature of the
solid resin (T.sub.g, .degree.C.)
______________________________________
TABLE II
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Copolymers containing hydroxyl groups
(quantities in g)
Copolymers B.sub.1 B.sub.2
______________________________________
Part I
Toluene 9000 9000
Part II
Methyl methacrylate 3660 4325
n-butylmethacrylate 2375 2690
Styrene 1870 1260
Hydroxyethyl methacrylate
1890 1420
Acrylic acid 100 100
Part III
tert.-Butylperoxy-2-ethyl-
440 580
hexanoate (70% in isododecane)
Toluene 665 625
Polymerization temperature (.degree.C.)
125 110
Solids content (%) 50.5 51.0
Viscosity at 23.degree. C. (mPa.s)
2365 1750
Glass transition temperature of
68 61
solid resin (T.sub.g, .degree.C.)
OH number of solid resin
80 60
(mg KOH/g)
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II. Preparation of a urea group- and urethane group-containing polyol
cross-linking agent B.sub.3
444 g of 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane, 168.5
g of acetone and 0.2 g of digutyl tin dilaurate were introduced into a
2-liter four-necked flask equipped with stirrer, reflux condenser and two
dropping funnels. the mixture was heated to 60.degree. C. with stirring
under a nitrogen atmosphere. A solution of 118 g of hexanediol-(1,6) in
168.5 g of acetone was then added dropwise within 2 hours at 60.degree. C.
and the reaction mixture was stirred at 60.degree. C. until the isocyanate
content of the reaction mixture was about 9.3%. The mixture was then
introduced into a dropping funnel and added dropwise at 20.degree. C.
within one hour to 150 g of 1-amino-2-propanol contained in a 2-liter
three-necked flask equipped with stirrer, reflux condenser and dropping
funnel. Stirring was continued until the isocyanate content of the
reaction mixture was<0.1%. The solvent was then distilled off as
completely as possible under vacuum and the product was dried to constant
weight in a vacuum drying cupboard at 80.degree. C. and 15 mbar. A
colorless solid having an OH content of 4.5% and a glass transition
temperature, T.sub.g (DTA) of 67.degree. C. was obtained.
III. Preparation of a powder coating composition according to the invention
Copolymers A.sub.1 to A.sub.4 were each melted and homogenized with a
polyol cross-linking agent B) and other auxiliary agents and additives C)
in a commercially available extruder. When the melt discharged from the
apparatus had solidified, the product was ground and sieved to remove
particles having a diameter larger than 0.1 mm and then applied to test
sheets by means of an electrostatic spray device and cured at 140.degree.
C. for 30 minutes.
The solvent resistance of the lacquer films, which were about 50 .mu.m in
thickness, was tested by a rubbing test using a wad of cotton wool soaked
in acetone. The result was given in the number of double rubs which could
be applied without visible change to the lacquer film. Not more than 50
double rubs per film were carried out.
Table III set forth the formulations in percentages by weight and the
solvent resistance as the degree of cross-linking.
TABLE III
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Formulations of the powder coating compostions
according to the invention in percent by weight
Formulation
1 2 3 4 5 6 7 8 9 10
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Copolymer A)
61.3 A.sub.1
62.5 A.sub.3
58.7 A.sub.2
62.5 A.sub.4
34.2 A.sub.1
29.2 A.sub.2
47.3 A.sub.3
29.0 A.sub.4
88.0
63.8 A.sub.1
Copolymer B) 35.1 B.sub.1
40.1 B.sub.2
Polyol cross- 22 35.5
linking agent B.sub.3
Crelan U 502.sup.1 40.3
THEIC.sup.2
8.0 6.8 6.8 11.3
2,2-bis-(4-hydroxy- 10.6
cyclohexyl)-propane
Modaflow P III.sup.3
0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7
Titanium dioxide
30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0
Acetone rubbing
50 50 42 48 50 50 46 50 50 50
test (number of
double rubs)
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.sup.1 an OH functional polyester having a hydroxyl content of about 1.5%
available from Bayer AG
.sup.2 N,N',N"-tris-(2-hydroxyethyl)-isocyanurate
.sup.3 a levelling agent available from Monsanto
Although the invention has been described in detail in the foregoing for
the purpose of illustration, it is to be understood that such detail is
solely for that purpose and that variations can be made therein by those
skilled in the art without departing from the spirit and scope of the
invention except as it may be limited by the claims.
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